Smart Solutions – Stormwater Management

Recent extreme weather events have once again raised debate about the best ways to ensure resilient and affordable stormwater management. Meanwhile, Patricia Moore reports that water sensitive urban design will become a more mainstream practice when the tangible benefits are better analysed and communicated.

Forget the grey – think green. Water sensitive urban design (WSUD) puts the spotlight on natural landscape and systems, rather than traditional pipes and culverts. And it is changing the way local authorities manage the challenges brought by a combination of issues including ageing infrastructure, intense weather events and limited funding.

Tim Fisher

In Auckland, the drivers are growth and the requirements of the Unitary Plan with assistance from Auckland Council Guidelines (GD01 & GD04). WSUD is fast becoming mainstream practice, says Tim Fisher, Tonkin + Taylor’s executive leader – engineering and principal water engineer.

“The Special Housing Areas have also given WSUD a significant boost. But for WSUD to become mainstream elsewhere, local governments will need to set up policy / planning frameworks to support it.

“More New Zealand research and case studies are needed to give developers, designers and councils the confidence to use WSUD in other regions.”

That’s a point reinforced by Harrison Grierson’s Michael Chapman, principal, team leader – water resources. “A growing number of robust and thorough cost-benefit examples will mean the industry can start embedding WSUD earlier in the design process.”

He sees uptake as “very much an evolutionary process” and inherent in the concept of water sensitive design.

“The philosophy,” he says, “will take time to evolve and mature as an emerging science. I think it will become mainstream as society in general moves towards designing systems that are regenerative rather than degenerative.”

“It will then become a priority rather than being implemented as part of regulatory requirements. It should be prioritised, as it provides an opportunity to improve receiving environment water quality while achieving social and cultural objectives.”

James Reddish

But, while WSUD is a better solution to reducing stormwater impacts, and one that’s gaining momentum worldwide, there are barriers slowing implementation, says James Reddish, principal environmental engineer with WSP Opus.

He lists: establishing policy supported by a strong evidence base; understanding costs; quantifying the non-economic benefits (cultural, social and environmental); raising awareness and recognising the need for education and training; and clarifying issues around potential changes of ownership and operation through the assets’ lifecycle.

Meanwhile, Tim says some of the best WSUD is coming from public / private collaboration.

“Ellerslie’s planned Element apartment complex, on which Tonkin + Taylor is working, is a good example. Element is driven by private investment but has been strongly enabled by Auckland Council.

“WSUD has allowed us to reduce stormwater discharges and potable water demand, reducing the impacts on infrastructure.”

James adds that although much of WSUD is delivered through land development, there are many examples of successful council initiatives.

These include Auckland’s Daldy and Halsey Street redevelopment and the Avon River Precinct / Te Papa Otakaro, the first anchor project for the Canterbury Earthquake Authority.

“However, small projects such as the Kowhai Reserve in Warkworth are just as important to demonstrate what is achievable.”

WASTEWATER OVERFLOWS

While ‘extreme’ weather events serve to highlight the inadequacies of current stormwater systems, it’s been reported that if there are more than five millimetres of rain in Auckland, combined storm and wastewater pipes contribute to overflows at 41 points around the Waitemata Harbour.

So should technology, such as low-cost internet of things water level meters and sensors connected via a low-power wide-area network (LPWAN), be playing a greater role in monitoring and managing such situations?

“There are wastewater overflows in just about every sewer system around New Zealand. While overflows commonly serve an important function to protect against sewage backups onto properties, it’s important to understand and manage the risk of effects on agreed community waterway uses and outcomes.

“Real-time monitoring of the overflows can provide a very useful tool in terms of assessing and managing the risk of effects.

Clint notes that the cost of real-time monitoring has come down substantially in the past decade.

“So utilities should be reviewing and assessing the use of a wider deployment of monitors to aid in better real-time risk management, improve proactive operational response measures, and to support development of more optimised long-term risk reduction measures.”

UNDERSTANDING CATCHMENTS

Vijesh points out that access to technology is not the problem. “Unfortunately, whatever technology is used you’ll still find most of our receiving environments are polluted.

“What’s needed is strong leadership that will deliver results in a short timeframe. The proposed water quality tax is a great start; something that should have been initiated 20 years ago.”

“NPS-UDC is about urban development which is as much about provision of infrastructure as it is about houses and commercial buildings,” he says.

“WSUD can help urban development in both the greenfield and brownfield contexts by reducing the size of new stormwater infrastructure or the upgrading of existing infrastructure and redistributing the costs for stormwater management.”

The answer, says Vijesh, is a whole-of-catchment approach. “It’s a smart solution and all that’s necessary to meet the requirements of the NPS-UDC. The challenges are not in the technical area but more in strategic leadership.

“The current piecemeal approach within a catchment doesn’t have real benefit to water quality when, and where, it actually matters – that is, right now and where you put your head into water.”

Michael notes that is it essential to understand each catchment.

“Rather than covering the land with impervious areas then piping runoff from those areas to nice-looking wetlands at the bottom of each sub-catchment, we need to understand the catchment and place wetlands only where they would naturally occur and therefore where they are easier to design and engineer.”

The good news is a desire in the industry to address existing barriers to the wider implementation of WSUD, reports James. “Importantly, it requires courage from decision-makers, designers and developers.

“If we can collectively learn from mistakes, and share data and good practice, implementation will be faster and
more successful.”